Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $114.36   6.548%   $121.8483   $121.85   $121.85   $121.80  
  Purchase #2 $55.33   4.195%   $57.6511   $57.65   $57.65   $57.70  
  Purchase #3 $67.39   9.495%   $73.7887   $73.79   $73.80   $73.80  
  Purchase #4 $16.73   6.520%   $17.8208   $17.82   $17.80   $17.80  
  Purchase #5 $68.51   9.830%   $75.2445   $75.24   $75.25   $75.20  
  Purchase #6 $230.56   6.414%   $245.3481   $245.35   $245.35   $245.30  
  Purchase #7 $200.86   5.516%   $211.9394   $211.94   $211.95   $211.90  
  7 purchase totals = $753.74       $803.6409   $803.64   $803.65   $803.50